The United States is one of Bolivia's top trade partners. U.S. exports to Bolivia include machinery, vehicles, aircraft, optical and medical instruments, and agricultural products. U.S. imports from Bolivia include silver and jewelry, crude oil, tin, Brazil nuts, and other agricultural products. Bolivia is generally open to foreign direct investment, but legal uncertainties include regulatory changes called for in the 2009 Bolivian constitution. The government nationalized numerous companies that were privatized in the 1990s. As of June 2012, the Bolivian Government terminated the U.S.-Bolivia bilateral investment treaty that entered into force in 2001, but the treaty will continue to apply for another 10 years to cover investments existing at the time of termination. While economic growth has been positive throughout the last decade, Bolivia remains one of the poorest countries in the Western Hemisphere.